The present invention relates to a substrate manufacturing apparatus including circuit patterns such as semiconductor devices and liquid crystal and particularly to the technique for inspecting the patterns of substrate in the course of the manufacture using SEM.
A pattern inspecting apparatus using the electron beam of the related art is described, for example, in the official gazette of Japanese Laid-Open Patent Application No. 258703/1993. An example of the pattern inspection apparatus using electron beam described in the above cited reference is illustrated in FIG. 1. An electron beam 2 emitted from an electron beam source 1 is deflected with a deflector 3 in the X direction, this electron beam irradiates an object substrate 5 via an objective lens 4, the secondary electron 7 (including the secondary electron and reflected electron generated from a sample through irradiation of the primary electron beam) emitted from the object substrate 5 is simultaneously deflected with an Exc3x97B deflector (hereinafter referred to as only Exc3x97B) 13 while a stage 6 is continuously moved in the Y direction, this secondary electron beam 7 is detected with a detector 8 as an electric signal and it is then amplified with a pre-amplifier 14, thereafter the detected signal is A/D-converted with an A/D converter 9 to obtain a digital image, this image is then compared with a digital image at the area which may be expected as to be identical in an image processing circuit 10, thereby an area generating a difference is detected as a pattern defect 11 to identify the defective area. The object substrate 5 is kept at a negative potential with the retarding voltage and therefore an acceleration voltage can easily be changed on the object substrate 5 by changing the retarding voltage 12.
In the apparatus of the related art as illustrated in FIG. 1, the secondary electron 7 has been detected with convergence to one detector 8. However, a degree of convergence of the secondary electron is restricted with various conditions. As the restricting conditions, it is possible to consider (1) degree of freedom of the electro-optical system (retarding voltage, current of primary beam, electric field of the area near the sample, etc. for controlling the acceleration voltage of the primary electron incident to the sample), (2) deflection of the electron beam 2 with the deflector 3 for scanning the sample, (3) allowance of setting, (4) contamination of surface of the detector 7 generated with collision of electron beam and (5) various aberrations in the electro-optical system, or the like.
Although depending on the practical design of the electro-optical system, the conditions (4) and (5) contribute to the degree of convergence of secondary electron and the minimum degree may be estimated as about 1 mm under the condition of the electro-optical system, that is, under the condition that the retarding voltage, current of primary beam and field at the area near the sample which control the acceleration voltage of the primary electron incident to the sample is fixed to only one condition. Moreover, the influence on the degree (2) of convergence of the secondary electron due to the scanning of the deflector 3 with the electron beam 2 appears as the movement of the converging position of about 0.5 mm, although depending on the scanning width and magnifying factor for the secondary electron. Moreover, in regard to the degree of freedom (1) of the optical system, a degree of convergence is changed for about 1 mm by the defocusing, although depending on the other conditions, when the retarding voltage 12, for example, is changed.
Moreover, in actual, since the optical axis of the secondary electron optical system is deviated, it can be estimated that the converging position is shifted by about 0.5 mm. When these factors are added, the diameter of about 3 mm is required for the effective light receiving surface of the detector to detect the secondary electron and when the allowance of setting (3) is considered, the diameter of 4 mm will be required for the effective light receiving surface of the photosensor.
Meanwhile, the frequency characteristic of detector is inversely proportional to the area of the detector. For example, in the case of the detector having the diameter of 4 mm, the cut-off frequency is only 75 MHz even when the design condition and operating condition are improved. On the other hand, when the diameter of detector is set to 2 mm, the cut-off frequency becomes about 150 MHz. However, as explained above, since the detector of the related art requires a diameter of 4 mm, response is possible only for 15 Msps (sps: sample per second) of the sampling frequency corresponding to the cut-off frequency of 75 MHz and it has been impossible to respond to the higher frequency.
The present invention can provide an inspection apparatus using SEM which can sufficient detect the secondary electron even at the sampling frequency higher than 150 Msps which has been difficult in the structure of the related art to sufficiently cover the detection of secondary electron.
The first means for embodying the present invention is illustrated in FIG. 2.
Here, the structure for solving the problems will be explained, for easier understanding, for detection at the 400 Msps rate under the assumption that a size of detector is 4 mm square (in above example, the diameter is set to 4 mm, but here the detector has the size of 4 mm square), cut-off frequency is 75 MHz and the cut-off frequency is inversely proportional to only the area. Of course, the numerical values also change depending on the internal structure and material of sensor, but these are not explained here. The contents explained above is the essential factors for the case where the target of speed is set to 400 Msps or more. Moreover, the number of detectors is set, for example, to four, but it is selected as the typical value of a plurality of detectors and the present invention is never limited only to the numerical value 4.
The first means is composed of an electron source 1 for generating the electron beam 2, a deflector 3 for deflecting the electron beam 2, an objective lens 4 for converging the electron beam 2 on the object substrate 5, a stage 6 for holding the object substrate 5 to apply the retarding voltage 12 for the scanning and positioning, Exc3x97B 13 for deflecting the secondary electron 7 emitted from the object substrate 5, a 4-split detector 20 of 2 mm square each for detecting the secondary electron 7 deflected with the Exc3x97B 13, preamplifiers 21a to 21d having the bandwidth of 200 MHz or higher connected to each detector, an A/D converter 22 of 400 Msps for adding and A/D-converts outputs of the preamplifiers 21a to 21d to obtain the digital image and an image processing circuit 10 for detecting, from the digital image, an area generating difference as a defect 11 through comparison with the digital image of the area intrinsically providing expectation for the matching of images.
In above structure, the electron beam 2 from the electron source 1 is deflected in the X direction with the deflector 3, this electron beam 2 irradiates the object substrate 5 via the object lens 4, the secondary electron 7 from the object substrate 5 is bent with Exc3x97B 13 for detection with the 4-split detector 20 while the stage 6 is continuously moved in the Y direction, the signal is A/D-converted to obtain the digital image after the signal of each split detector into voltage with the preamplifiers 21a to 21d and the signals are added with the A/D converter and the image processing circuit 10 detects the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for the matching of images. In this case, the secondary electron 7 can be expanded only to the maximum area of 4 mm square even when change of retarding voltage 12 and deflection with the deflector 3 are considered.
Since the 4-split detector 20 is completed in 4 mm square with four detectors, while one detector is completed in 2 mm square, the secondary electron 7 enters any one of the sensors. The signal of any detector is received with the preamplifiers 21a to 21d and these signals are added in the A/D converter 22 to A/D-convert all secondary electrons 7. Since each detector is completed in the 2 mm square, the cut-off frequency is set to 300 MHz, bandwidth of the preamplifier is set to 200 MHz and A/D converter is set to 400 Msps, the detector, preamplifier and A/D converter are designed to cover 400 Msps and sufficient consideration is taken for 400 Msps.
When a 6-split or 8-split and moreover 12-split detector is used in place of the 4-split detector to provide the structure to detect the secondary electron, area of each detector can further be reduced and moreover it is now possible to further quickly detect the secondary electron than 400 Msps explained above.
Next, the second means for embodying the present invention is illustrated in FIG. 3 and is composed of an electron beam source 1 for generating the electron beam 2, a deflector 3 for deflecting the electron beam 2, an objective lens 4 for converging the electron beam 2 on the object substrate 5, a stage 6 for holding the object substrate 5 to apply the retarding voltage 12 for scanning or positioning, Exc3x97B 13 for bending the secondary electron 7 from the object substrate 5, a secondary electron deflector 30 for deflecting the secondary electron 7 bent with Exc3x97B 13, 4-split detectors 31a to 31d each of which has the 4 mm square size for detecting the secondary electron or the like deflected with the secondary electron deflector 30, preamplifiers 32a to 32d of 50 MHz bandwidth connected to each detector, A/D converters 33a to 33d of 100 Msps for converting the outputs of preamplifiers 32a to 32d to the digital image and an image processing circuit 10 for detecting, from the digital image, an area generating difference as the defect 11 through comparison with the digital image of the area providing expectation for the matching of images.
With introduction of such structure, the electron beam 2 from the electron beam source 1 is deflected in the X direction with the deflector 3 to irradiate the object substrate 5 via the objective lens 4, the secondary electron 7 from the object substrate 5 is bent with Exc3x97B 13 while the stage 6 is simultaneously moved continuously in the Y direction, thereafter the secondary electron deflector 30 is driven with 100 MHz to sequentially scan each detector of the 4-split detector 20 for detection with the 4-split detector 31, the signal obtained is then amplified with the preamplifiers 32a to 32d and the signal of each split detector is converted to the voltage, the signal is then A/D-converted to the digital image signal with the A/D converters 33a to 33d and the image processing circuit 10 compares the digital image with that of the area intrinsically providing the expectation for matching of the image and detects the area generating difference as the defect 11. In this case, the secondary electron 7 can be spread in maximum to the area of 4 mm square even when considering, for example, the change of retarding voltage 12 and deflection by the deflector 3.
Since each 4-split sensor has the size of 4 mm square, the secondary electron 7 is all incident to the detector selected with the secondary electron deflector 30. The signal of any detector is received with the pre-amplifiers 32a to 32d and these signals are then A/D-converted with the A/D converters 33a to 33d. The detector has a size of 4 mm square, cut-off frequency is 75 MHz, bandwidth of preamplifier is 50 MHz and the A/D converter has 100 Msps. Therefore, the detector, preamplifier and A/D converter is responsible to 100 Msps and moreover the sampling is conducted once for four pixels at 100 Msps. Accordingly, sufficient consideration for 400 Msps can be made with the total function of pairing of four detectors, preamplifiers and A/D converters.
Operations of the secondary electron deflector 30 will be explained in detail with reference to FIG. 10. The secondary electron deflector 30 is switched, in units of 2.5 ns, in the sequence of a, b, c, d with the period of 100 MHz. The A/D converter 33 samples the signal in the 10 ns period and 100 Msps and obtains in total 400 Msps by sequentially arranging the outputs of the four A/D converters.
Operating method of the secondary electron deflector 30 will be explained with reference to FIG. 11. The circle scanning 92 for continuously moving the secondary electron 7 on the detecting surfaces of the 4-split detectors 31a to 31d can be realized by defining respectively the X/Y deflection signals as sin/cos signals. Moreover, the switching scanning 93 for discretely scanning the secondary electron 7 on the detecting surfaces of the 4-split detectors 31a to 31d can also be realized by defining the X/Y deflection signals as the square waves of 10 ns period resulting in the deviation of phase of 90 degrees. In addition, although not illustrated, the similar signals can also be obtained by defining the X/Y deflection signal as the square waves of 10 ns and 5 ns periods.
The third means for embodying the present invention is illustrated in FIG. 4 and is composed of an electron beam source 1 for generating the electron beam 2, a deflector 3 for deflecting the electron beam 2, an objective lens 4 for converging the electron beam 2 on the object substrate 5, a stage 6 for holding the object substrate 5 to apply the retarding voltage 12 for scanning or positioning, an Exc3x97B 13 for bending the secondary electron 7 from the object substrate 5, a 4-split smart detector 40 each of which has a size of 2 mm square integrating a preamplifier and an adder for detecting the secondary electron 7 bent with the Exc3x97B 13, an A/D converter 41 of 400 Msps for converting an output of the 4-split smart detector 40 into a digital image and an image processing circuit 10 for detecting, from the digital image, the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for matching of images.
With introduction of this structure, the electron beam 2 from the electron beam source 1 is deflected in the X direction with the deflector 3 to irradiate the object substrate 5 via the objective lens 4, the secondary electron 7 from the object substrate 5 is bent with the Exc3x97B 13 while simultaneously moving the stage 6 in the Y direction continuously, thereafter the electron beam 7 is then detected with the smart detector 40 and A/D-converted into the digital image with the A/D converter 41 and the image processing circuit 10 detects, from the digital image, the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing the expectation for matching of images.
In this case, the secondary electron 7 can be spread in maximum up to the area in size of 4 mm square even when considering the change of retarding voltage 12 and deflection with the deflector 3. Since one 4-split sensor as the size of 2 mm square and the four sensors also have the size of 2 mm square, the electron beam is incident to any one of the four sensors. The signal of any detector is received with a preamplifier provided to each sensor built in the smart detector 40 and the signal of all secondary electrons 7 can be obtained as the output of the smart detector 40 by adding such signals from the detector. When the bandwidth of the preamplifier built in the smart detector 40 is set to 200 MHz, since the detector has the size of 2 mm square, the cut-off frequency is 300 MHz and A/D converter has 400 Msps, the detector, preamplifier and A/D converter are responsible to 400 Msps because of sufficient consideration for 400 Msps.
The fourth means for embodying the present invention is illustrated in FIG. 5 and is composed of an electron beam source 1 for generating the electron beam 2, a deflector 3 for deflecting the electron beam 2, an objective lens 4 for converging the electron beam 2 on the object substrate 5, a stage 6 for holding the object substrate 5 to apply the retarding voltage 12 for scanning or position, a Exc3x97B 13 for bending the secondary electron 7 from the object substrate 5, a converging optical system 51 for converging the secondary electron 7 bent with the Exc3x97B 13, a detector 8 of 2 mm square for detecting the secondary electron 7 converged with the converging optical system 51, a preamplifier 52 having the bandwidth of 200 MHz or more connected to the detector, an A/D converter 9 of 400 Msps for converting an output of the preamplifier 52 to the digital image through the A/D conversion and an image processing circuit 10 for detecting, from the digital image, the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for matching of images.
With introduction of the structure explained above, the electron beam 2 from the electron beam source 1 is deflected in the X direction with the deflector 3 to irradiate the object substrate 5 via the objective lens 4, the secondary electron 7 from the object substrate 5 is bent with the Exc3x97B 13 having optimized the bending angle for each retarding voltage while simultaneously moving continuously the stage 6 in the Y direction, thereafter the secondary electron 7 converged to the position depending on the retarding voltage with the converging optical system 51 is detected with the detector 8 of 2 mm square, the signal is then amplified with the preamplifier 52 and A/D-converted to the digital image with the A/D converter 9 and the image processing circuit 10 detects the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for matching of images.
In this case, the spreading by defocusing and movement of converging position when the retarding voltage 12 is changed are respectively adjusted with the converging optical system 51 and Exc3x97B 13. Therefore, even when deflection by the deflector 3 is considered, the secondary electron 7 is spread in maximum up to the area of 1.5 mm square+design allowance. Here, the detector 8 is rather small in size because one detector has the size of 2 mm square but since the electron beam is incident to the detector, the signal of almost all secondary electrons 7 can be obtained as an output of the detector 8. When the bandwidth of preamplifier is set to 200 MHz, since the detector has the size of 2 mm square, cut-off frequency is 300 MHz, A/D converter has 400 Msps, the detector, preamplifier and A/D converter are responsible to 400 Msps with sufficient consideration for 400 Msps.
The fifth means for embodying the present invention is illustrated in FIG. 6 and is composed of an electron beam source 1 for generating the electron beam 2, a deflector 3 for deflecting the electron beam 2, an objective lens 4 for converging the electron beam 2 on the object substrate 5, a stage 6 for holding the object substrate 5 to apply the retarding voltage 12 for scanning or positioning, an Exc3x97B 13 for bending the secondary electron 7 from the object substrate 5, detectors 61a to 61b in size of 2 mm square provided in a plurality of positions for detecting the secondary electron 7 bent with the Exc3x97B 13, preamplifiers 62a to 62b having the bandwidth of 200 MHz or higher connected to each detector, a signal combining circuit 63 for adding or switching outputs of the preamplifiers 62a to 62b, an A/D converter 9 of 400 Msps for converting the signal combined with the signal combining circuit 63 into the digital image and an image processing circuit 10 for detecting, from the digital image, the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for matching of images.
With introduction of such structure, the sharing range of the retarding voltage 12 of the detector 61a is defined as Vamin to Vamax and the sharing range of the retarding voltage 12 of the detector 61b is defined as Vbmin to Vbmax, the detectors 61a to 61b are provided at the converging distance of the secondary electron 7 corresponding to the retarding voltage 12 of the sharing range with the setting for covering the range of all retarding voltages 12 when these are added. When the retarding voltage 12 is in the range of Vamin to Vamax, the detector 61a is selected with the signal combining circuit 63 and Exc3x97B 13 is set to apply the electron beam to the detector 61a. 
The electron beam 2 emitted from the electron beam source 1 is deflected in the X direction with the deflector 3 to irradiate the object substrate 5 via the objective lens 4, the secondary electron 7 from the object substrate 5 is then bent with the Exc3x97B 13 having optimized the bending angle while simultaneously moving continuously the stage 6 in the Y direction, thereafter the secondary electron 7 is then detected with the detector 61a in the size of 2 mm square and is then amplified with the preamplifier 62a, thereafter the signal is A/D-converted to the digital image in the A/D converter 9 because the detector 61a is selected in the signal combining circuit and the image processing circuit 10 detects, from the digital image, the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for matching of images.
In this case, since the spread by defocusing and movement of converging position when the regarding voltage 12 is changed are adjusted with selection of the detectors 61a to 61b and adjustment with Exc3x97B 13, the secondary electron 7 can be spread in maximum to the area of 1.5 mm square+design allowance even when considering the deflection with the deflector 3. Since one detector of 61a to 6b has the size of 2 mm square with smaller allowance and the electron beam enters the detector, the signal of almost all secondary electrons 7 can be obtained as an output of the detectors 61a to 61b. When the bandwidth of the preamplifier is set to 200 MHz, since the sensor has the size of 2 mm square, cut-off frequency is 300 MHz and A/D converter has 400 Msps, the detector, preamplifier and A/D converter are responsible to 400 Msps with sufficient consideration for 400 Msps.
The sixth means for embodying the present invention is illustrated in FIG. 7 and is composed of an electron beam source 1 for generating the electron beam 2, a deflector 3 for deflecting the electron beam 2, an objective lens 4 for converging the electron beam 2 on the object substrate 5, a stage 6 for holding the object substrate 5 to apply the retarding voltage 12 for scanning or positioning, a Exc3x97B 13 for bending the secondary electron 7 from the object substrate 5, a secondary electron returning deflector 71 for deflecting the secondary electron 7 bent with the Exc3x97B 13, a detector 72 in size of 2 mm square for detecting the secondary electron 7 returned with the returning deflector 71, a preamplifier 73 having the bandwidth of 200 MHz or more connected to the detector 72, an A/D converter 9 of 400 Msps for A/D-converting the output of preamplifier 73 to the digital image and an image processing circuit 10 for detecting, from the digital image, the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for matching of images.
With introduction of the structure explained above, the electron beam 2 from the electron beam source 1 is deflected in the X direction with the deflector 3 to irradiate the object substrate 5 via the objective lens 4, the second electron 7 from the object substrate 5 is bent with the Exc3x97B 13 having optimized the bending angle for each retarding voltage while simultaneously moving the stage 6 continuously in the Y direction, thereafter the secondary electron 7 is detected with the detector 72 in the size of 2 mm square by returning amount of movement on the detector 72 at the deflector 3 with the secondary electron returning deflector 71 in order to eliminate movement of secondary electron 7 and this secondary electron 7 is then amplified with the preamplifier 73, thereafter the signal is A/D-converted to the digital image with the A/D converter 9 and the image processing circuit 10 detects the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for matching of images.
In this case, movement of converging position when the retarding voltage 12 is changed is adjusted with the Exc3x97B 13. Moreover, since the secondary electron returning deflector 71 is used for movement of the secondary electron 7 resulting from the scanning of the deflector 3, the secondary electron 7 is spread in maximum only up to the area of 2 mm square+design allowance. The detector 72 does not have allowance because it has the size of 2 mm square, but since the electron beam is incident to the detector, the signal of the secondary electron 7 can be defined as the output of the detector 72. When the bandwidth of preamplifier is set to 200 MHz, since the detector has the size of 2 mm square, cut-off frequency is 300 MHz and A/D converter has 400 Msps, the detector, preamplifier and A/D converter are responsive for 400 Msps with sufficient consideration for 400 Msps. This structure cannot achieve the target with itself but it is possible to use this structure to attain the design allowance through combination, for example, with the structure of the fifth means.
The seventh means for embodying the present invention is illustrated in FIG. 8 and is composed of an electron beam source 1 for generating the electron beam 2, a deflector 3 for deflecting the electron beam 2, an objective lens 4 for converging the electron beam 2 on the object substrate 5, a stage 6 for holding the object substrate 5 to apply the retarding voltage 12 for scanning or positioning, a Exc3x97B 13 for bending the secondary electron 7 from the object substrate 5, a reflector 81 for collision with the secondary electron 7 bent with the Exc3x97B 13, a converting optical system 83 for converging the secondary electron 82 generated with the secondary electron 7 collided with the reflector 81, a detector 84 of 2 mm square for detecting the secondary electron 82 converged with the converging optical system 83, a preamplifier 85 having the bandwidth of 200 MHz or higher connected to the detector 84, an A/D converter 9 of 400 Msps for A/D-converting output of the preamplifier 85 to the digital image and an image processing circuit 10 for detecting, from the digital image, the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for matching of images.
In the structure of the detector using a plurality of detectors, those having reduced, as much as possible, the non-effective area in the periphery of the detector is provided adjacently. At least non-effective area of 0.2 mm is required when it is reduced as much as possible. When these are allocated without any interval, the detectors maybe allocated by providing the non-effective area of 0.4 mm. In this method, a plurality of detectors may be integrated at the time of manufacturing the detector. Although depending on the process, it is possible to provide the non-effective area of 0.02 mm or less. FIG. 9 illustrates an example where five detectors 91a to 91e are used as the detector.
With introduction of the structure explained above, the electron beam 2 from the electron beam source 1 is deflected in the X direction with the deflector 3 to irradiate the object substrate 5 via the objective lens 4, the secondary electron 7 from the object substrate 5 is bent with the Exc3x97B 13 having optimized the bending angle for each retarding voltage, thereafter the secondary electron 7 is collided with the reflector 81 and the secondary electron 82 generated at the reflector 81 is then detected with the detector 84 of 2 mm square via the converging optical system 83, the signal is amplifier with the preamplifier 85 and is then A/D-converted to the digital image of the A/D converter 9 and the image processing circuit 10 detects the area generating difference as the defect 11 through comparison with the digital image of the area intrinsically providing expectation for matching of images.
In this case, since the electron beam 7 is once collided with the reflector 81, the secondary electron 82 almost having no energy is generated not depending on the retarding voltage 12 and scanning by the deflector 3 and this secondary electron 82 is inputted to the detector 84 with the converging optical system 83. Accordingly, the secondary electron 82 is spread in maximum to the area of 2 mm square. Since the detector 84 has the size of 2 mm square, the signal of all secondary electron 7 can be obtained as the output of detector 84. When the bandwidth of a preamplifier is set to 200 MHz, since the detector is in the size of 2 mm square, cut-off frequency is 300 MHz and A/D converter has 400 Msps, the detector, preamplifier and A/D converter are responsible for 400 Msps with sufficient consideration for 400 Msps.
In the means and operation to solve the problems explained above, the converging position to the detector is adjusted with Exc3x97B, but it is also possible to realize the function to adjust the position of secondary electron or the like to the detector by inserting the secondary electron deflector in the optical path of only the secondary electron, in place of allowing both the electron beam and secondary electron to pass the circuits other than Exc3x97B. Moreover, since a large aberration is generated if the electron beam is deflected to a large extent with the Exc3x97B, it can be thought to cancel the aberration by adding a dummy Exc3x97B for operating in the inverse direction.
These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.